Infusion pumps are devices used to pump fluid medications into a patient in a controlled manner. One specific type of infusion pump is the insulin pump, which is used for the administration of insulin in treating patients with diabetes mellitus, a process also known as continuous subcutaneous insulin infusion (CSII) therapy. Typically, an infusion pump includes a pump (which includes controls, a processing module, and batteries), a reservoir containing fluid medication (e.g. insulin), an infusion set (which includes a cannula and/or catheter for subcutaneous insertion into the patient and a tubing system connecting the reservoir to the cannula/catheter. Upon insertion into a patient, the infusion set (more particularly the inserted cannula) is typically maintained in a transcutaneous position at the infusion site for multiple days to allow for continuous delivery of fluid medication. Cannulas and catheters provide passageways for delivering the medication to the patient.
A persistent problem associated with such devices is that the human body spontaneously reacts against foreign bodies which are introduced into the body, such as an implanted cannula (including plastic catheter or metal needle), (see, e.g. U.S. Pat. No. 5,219,361). Among the various responses of a body to foreign bodies, inflammation and the build-up of fibrous tissue at the infusion site significantly shortens the duration that an infusion set may be maintained at a single infusion site (i.e. “site-loss”). Moreover, tissue encapsulation and blockage of the implanted cannula or catheter (i.e. “occlusion”) often occurs, thereby impeding or halting infusion of medication. Thus, frequent re-positioning of the infusion site for continued usage of the infusion pump is required.
Patients may also experience scar tissue buildup around an inserted cannula, resulting in a hard bump under the skin after the cannula is removed. The scar tissue does not heal particularly fast, so years of wearing an infusion pump and changing the infusion site will result in a decrease of viable infusion sites. Furthermore, for example with diabetic patients, the areas with scar tissue build-up generally have lower insulin sensitivity, which in turn may affect basal rates and bolus amounts. In some extreme cases, the delivery of insulin will appear to have little to no effect on lowering blood glucose levels and require a change in the infusion site location.
A patient's own natural defense systems can frustrate the controlled delivery of fluid medications to a patient's tissue. Thus, there is a need for methods and systems that can inhibit the human foreign-body response to implanted medical devices such as the inserted cannulas or catheters.